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M. G. Baring, A. K. Harding (NASA Goddard Space Flight Center)
Developments over the last couple of years have supported the interpretation that anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) possess unusually high magnetic fields, and furthermore may represent a class or classes of neutron stars distinct from the population of conventional radio pulsars. We have recently suggested that such a dichotomization of the pulsar population may naturally arise due to the inherently different conditions in subcritical and supercritical magnetic fields. We summarize, within the polar gap model, expectations for observable properties of highly magnetized pulsars, conventional or anomalous, including the physics that can explain radio quiescence in AXPs and SGRs, including trends in luminosity and spectral shape as pulsar fields increase above 1013 Gauss. We discuss potential suppression of pair production and cascade generation in very strong fields by photon splitting and by threshold pair creation, as well as issues of positronium formation. The roles of the polar gap acceleration and the primary photon emission mechanism are also addressed. X-ray and hard gamma-ray spectral and observability properties are identified, with a view to establishing goals for future high energy experimental programs.
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